Combined air and evaporator temperature control means for air conditioner apparatus

ABSTRACT

In an air-conditioning apparatus, a single temperature sensor is used to control both room temperature and to prevent evaporator icing by mounting the sensor in heat conducting relation to the evaporator and in a path of airflow which parallels but bypasses the main stream of air through the evaporator.

ited States Patent Moy 1 Jan. 25, 1972 COMBINED AIR AND EVAPORATOR [5 1 References Cited TEMPERATURE CONTROL MEANS UNITED STATES PATENTS FOR AIR CONDITIONER APPARATUS 2,419,377 4/1947 Shaw ..62/214 Inventor: Harry E y San Antonio, x- 2,947,153 8/1960 Atchison.... ..62/156 D 3,411,311 11/1968 Wegman.... ...62/229 [73] Asslgnee' i nf r Incommed San 2,421,258 5/1947 Goddard ..62/214 [22] Filed: May 18, 1970 Primary Examiner-Meyer Perlin pp No 38 190 Attorney1(emon, Palmer& Estabrook [57] ABSTRACT [52] US. Cl ..62/2l5, 62/227, 66220222692, In an aipconditioning apparatus, a Single temperature Sensor m Cl F25, 1/00 is used to control both room temperature and to prevent evaporator icing by mounting the Sensor in heat conducting [58] Flew of Search relation to the evaporator and in a path of airflow which parallels but bypasses the main stream of air through the evaporator.

3 Claims, 4 Drawing Figures COMBINED AIR AND EVAPORATOR TEMPERATURE CONTROL MEANS FOR AIR CONDITIONER APPARATUS BACKGROUND OF THE INVENTION A problem which often arises with air conditioners is the formation of frost and even solid ice on the evaporator surfaces. There are multiple factors which effect frost buildup and these include outside ambient temperatures, relative humidity and refrigerant level. For obvious economic reasons it is desirable to utilize a single thermostat for controlling both the temperature of the space to be cooled and the defrosting or preventing of frost on the evaporator surfaces. Single tem-' perature sensor thermostat control means for this purpose are known and examples may be found in US. Pat. Nos. 2,947,153 and 3,158,005. In both of these patents a single temperature sensor is positioned adjacent to and directly in the main stream of air flowing from the space to be cooled to the evaporator. Also in each of these patents, the effect of actual evaporator temperature on the temperature of the bulb is automatically increased in response to frost buildup between the fins on the evaporator coils due to the reduction in airflow through the coil and across the temperature sensing means. Effectively therefore the controls of these two prior patents are dependent upon actual formation of frost and the reduction of airflow as a direct result thereof before the sensing means is effective to cycle off the compressor and permit the evaporator to defrost.

It is the principal object of the present invention to provide a single temperature sensing control means which while generally of the type shown in the aforementioned patents, is effective to cycle the compressor off prior to the formation of any substantial amount of frost on the fin surfaces of the evaporator coils.

BRIEF SUMMARY OF THE INVENTION One way to achieve the aforementioned object is to place the temperature sensing means in heat conducting relationship with the evaporator coils proper but at the same time to remove it from the main stream of room air returning to the evaporator and' place it instead in a location which is effectively a bypass for the main stream of return air. The room air therefore contacts the temperature sensor and then reenters the main stream of return air downstream of the evaporator. Efi'ectively this affords a better control of evaporator temperature and during normal operation, the evaporator remains substantially above the freezing point of water.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic showing of the basic components of a room-type air conditioner with a temperature control means located in accordance with the present invention;

FIG. 2 is a more detailed view of the actual mounting of the temperature sensitive bulb for the thermostat; and

FIGS. 3 and 4 are details of the actual mounting structure for the temperature sensitive bulb on a return bend of the evaporator structure.

DETAILED DESCRIPTION OF THE DRAWINGS The invention as shown in the accompany drawings and as described hereinafter will be as applied to a conventional window unit type of room air conditioner although it will be readily appreciated by those skilled in this art that the control means forming the subject of the invention is applicable to air conditioners or refrigeration apparatus generally.

Turning first to FIG. 1 of the drawings, a rather diagrammatic showing includes the conventional compressor 10, condenser l2 and evaporator 14 connected in the usual series circuit, the condenser and evaporator being connected through a capillary 16 or other appropriate expansion control device. The entire unit is contained within an outer housing 18, the interior of which is divided by a partition 20 into warm and cool compartments which house the compressor 10 and the condenser 12 and evaporator 14, respectively. Conveniently, although not necessarily a pair of fans 22 and 24 are mounted on the same shaft of a motor 26. The fan 24, of course, is effective to establish a flow of air from the space to be cooled over the cold surfaces afforded by the fins on the tubes in the evaporator 14 and the cooled air is then returned to the space from which it was originally drawn. The fan 22, on the other hand, circulates outside air over the coils of the condenser unit 12 in order to remove heat absorbed by the refrigerant during its passage through the evaporator 14 as well as heat added by the compressor 10.

The economic advantages of having a single temperature sensing element to control both defrosting of the evaporator and the temperature of the room air are carefully pointed out in the aforementioned prior US. Pat. No. 2,947,153. The temperature sensing bulb of the present invention is shown in FIG. 1 at 28. The bulb is connected through a closed fluid conduit 30 to a conventional bellows structure 32 which is effective to open and close the contacts 34 connected in series with the electrical supply to the compressor 10. The setting of the thermostat control means is by way of a conventional mechanical biasing arrangement for the contacts 34 which is operated by means of a manually operated knob 36 placed on the control panel of the unit.

Turning now to FIGS. 2, 3 and 4 of the drawings for a detailed disclosure of the mounting of the temperature sensitive bulb 28, it will be seen first of all that the bulb is mounted adjacent one end of the evaporator 14 within a relatively closed compartment. This compartment adjoins one end of the evaporator 14 and the return bends 38 of the evaporator tubes extend into this same compartment. The bulb 28 is mounted in a vertical position by means of a heat conductive strap 40 which is either brazed directly to, or firmly clamped upon, one of the return bends 38. A plastic support block 42 is bolted directly to the strap 40 and houses a portion of the bulb 28, supporting the bulb so that at least a portion is directly exposed to the temperature of the strap 40 by being positioned immediately adjacent the bent semicircular end portion 44 of the strap. The plastic support block 42 also includes a passageway 46 for housing a conventional electrical resistor type of heat anticipator now in common use with thermostats of this type. A substantial remaining portion of the bulb 28 is enclosed in a sleeve of thermal insulating material such that the ultimate temperature of the bulb 28 during normal operation is primarily a function of the room air flow over the bulb. As soon as evaporator temperature drops below a predetermined point, however, the temperature of the bulb is sufficiently lowered to open the contacts 34 and deenergize the compressor motor to permit warming of the evaporator by the continued flow of room air thereover under the influence of v the fan 24.

In order to provide for a flow of room air over the bulb which flow is unaffected by frost buildup on the evaporator, a slot 50 is formed in an upper surface of the control panel closure and a further opening 52 may be provided near the base of the same enclosure. Further openings 54 are provided in a wall of the compartment adjacent the rear face of the evaporator 14. Due to the air pressure drop across the evaporator created by the fan 24, some room air will enter the control compartment through the openings 50 and 52 and this same air will contact the exposed portions of the bulb 28 and then exit through the openings 54 to the rear side of the evaporator. This air then mixes with the cooled air which has been drawn through the evaporator by the fan 24 and is reinjected into the space to be cooled.

While it is convenient to install the thermostat as hereinbefore described and particularly when it is used in conjunction with a heat anticipator of the type shown in US. Pat. No. 3,474,639, the described location minimizes the necessary electrical wiring. It will be appreciated, however, that it is entirely possible to locate the temperature sensitive bulb adjacent the front or upstream face of the evaporator provided the'mounting is such as to provide adequate thermal conduction between an evaporator coil and the temperature sensitive bulb.

in either location, it will be appreciated that it is possible to control the evaporator temperature in such a way as to prevent frost buildup rather than to first permit such buildup and then effect a defrosting operation. Generally, frost buildup will occur when evaporator temperatures are down to a level of the order of 25 or 26 F., whereas frost buildup will not occur if the temperature is maintained above that level. This, of course, is true because of the continued flow of warm air over the fins which surround the evaporator coils.

It is believed that it will be apparent to those skilled in this art that by locating the temperature sensitive bulb 28 as shown and described herein, that the bulb can be made to function in a manner which is specifically different from the control function which the equivalent bulb exercises in the systems shown in the aforementioned prior patents. Specifically, the bulb will act to turn off the compressor as soon as the evaporator temperature falls below a predetermined level, for example, 28, so that the actual formation of frost on the fins of the evaporator tubes is effectively prevented. The single bulb control systems of the prior art are dependent upon the formation of frost and a decrease in air flow for their operation.

While a preferred embodiment of the present invention as applied to a window mounted room air conditioner has been herein shown and described, applicant claims the benefit of a full range of equivalents within the scope of the appended claims.

lclaim:

1. in combination with an air conditioner of the compressor-condenser-evaporator type, a single control means for cycling the compressor on and off in accordance with both the temperature of the space to be cooled and the temperature of the evaporator, said control means comprising:

thermostat means including a switch connected in series with the electrical supply to said compressor, and a temperature sensitive bulb for operating said switch; means mounting said bulb in heat conductive relation to at least one coil of said evaporator; and

means for establishing a flow path for air from the space to p be cooled, over said temperature sensitive bulb and then to the downstream side of said evaporator, said path bypassing the main stream of return air through said evaporator; whereby the temperature of said bulb becomes a function of both the air from the space to be cooled and the evaporator temperature and said compressor is cycled to control room air temperature as well as preventing icing of said evaporator.

2. The combination defined by claim 1 in which said last mentioned means includes a substantially closed compartment adjacent one end of said evaporator, said compartment containing said temperature sensitive bulb therein and having an opening adjacent the upstream side of said evaporator for directing the air from said space to be cooled over said temperature sensitive bulb and a further opening adjacent the downstream side of said evaporator for directing said air into the stream of air that has moved through said evaporator.

3. The combination defined by claim 2 in which said temperature sensitive bulb is mounted in heat conducting relation to a return bend of said evaporator. 

1. In combination with an air conditioner of the compressorcondenser-evaporator type, a single control means for cycling the compressor on and off in accordance with both the temperature of the space to be cooled and the temperature of the evaporator, said control means comprising: thermostat means including a switch connected in series with the electrical supply to said compressor, and a temperature sensitive bulb for operating said switch; means mounting said bulb in heat conductive relation to at least one coil of said evaporator; and means for establishing a flow path for air from the space to be cooled, over said temperature sensitive bulb and then to the downstream side of said evaporator, said path bypassing the main stream of return air through said evaporator; whereby the temperature of said bulb becomes a function of both the air from the space to be cooled and the evaporator temperature and said compressor is cycled to control room air temperature as well as preventing icing of said evaporator.
 2. The combination defined by claim 1 in which said last mentioned means includes a substantially closed compartment adjacent one end of said evaporator, said compartment containing said temperature sensitive bulb therein and having an opening adjacent the upstream side of said evaporator for directing the air from said space to be cooled over said temperature sensitive bulB and a further opening adjacent the downstream side of said evaporator for directing said air into the stream of air that has moved through said evaporator.
 3. The combination defined by claim 2 in which said temperature sensitive bulb is mounted in heat conducting relation to a return bend of said evaporator. 